Gear pumps are widely used in a variety of applications and typically include a housing having an interior pumping chamber which may take on any of a variety of configurations such as an eight-shape or an oval-shape. A pair of meshed gears are disposed within the pumping chamber and are mounted on or are integral with shafts suitably journalled in the housing. On one side of the point whereat the gears mesh there will be provided an inlet and on the opposite side of the point of meshing, an outlet.
Upon rotation of one of the shafts, the gears will rotate in opposite directions drawing fluid, normally a liquid, into the pumping chamber through the inlet and conveying such fluid about the periphery of the chamber in the space between the gear teeth. When the point of meshing is reached, the fluid is forced out of the spaces between the teeth and out of the outlet of the housing.
The input drive shaft for a gear pump must be capable of accepting substantial misalignment between the drive member and the pump elements. This capability can be achieved with a quill shaft with suitable adapters on each end, generally splines, to interconnect the pump elements and the drive member. Lubricating the pump end adaptor with the working fluid raises the need for a rotating shaft seal with one seal member being a radial flange on the quill shaft. The need for the quill shaft to operate in a misaligned condition hence causes the shaft seal to also operate with misalignment.
Since the quill shaft is exposed to the pump working fluid on the pump end, it also is exposed to the pressure of the working fluid which is normally considerably higher than ambient pressure on the drive side of the seal. This pressure differential causes an axial force equal to the pressure differential times the shaft seal projected area. The substantial load thus generated must be opposed by a thrust bearing which is built into the shaft seal such that the seal performs the functions of shaft seal and thrust bearing, and is able to articulate with the shaft misalignment to maintain contact of the bearing and seal members. Such high load can cause the various components of the seal/bearing members to deflect and/or distort which in turn can result in undesirable uneven loading of various components which in turn may result in accelerated wear and/or premature failure.
By way of example, FIG. 1 illustrates a thrust bearing and seal construction made according to the prior art. A shaft 10 has one end 12 which is adapted to be connected to a rotary drive means or the like, exterior of a pump housing 14. The other end 16 of the shaft is adapted to drive, through an articulatable joint, a gear (not shown) within the pumping chamber (not shown) of the pump in a conventional fashion. Intermediate the ends 12 and 16 is an annular flange 18, the side 20 of which facing the shaft end 12 defines an annular bearing shoulder.
The housing 14 includes an opening 22 which receives a generally cup-shaped bearing and seal housing 24. The housing 24 has a cylindrical outer wall 26 within the opening 22 and a cylindrical inner wall 28 in close proximity to the shaft 10. A combined bearing and seal, generally designated 30, surrounds the shaft 10 and is disposed between the inner and outer walls 28 and 26 for generally free axial movement toward and away from the bearing shoulder 20. A compression coil spring 32 interposed between the bearing and seal 30 and the housing 24 biases the former toward the shoulder 20. A gimball washer 34 is also disposed within the housing 24 and is sandwiched between the housing 24 and the bearing and seal 30. The same allows the bearing and seal 30 to cant with universal movement within the housing 24.
In the prior art construction, at the radially inner diameter of the bearing and seal 30 adjacent the shoulder, there is located an annular sealing surface 36 which typically will be formed of carbon or the like. Immediately radially outwardly of the sealing surface 36 is a carbon thrust bearing pad 38. Differing or identical forms of carbon may be used in forming the components 36 and 38 as desired.
In any event, when the shoulder 20 is not distorted or deformed as a result of forces typically occurring within the pump, the same will occupy the solid line position illustrated in FIG. 1. As a consequence, the sealing surface 36 and the bearing pad 38 are substantially uniformly loaded. However, when axial thrust loads are applied along the shaft 10, the shoulder 20 may tend to become convex as the load attempts to literally extrude the flange through the bearing and seal 30. An exaggerated showing of such an occurrence is shown in dotted lines and designated 20' in FIG. 1.
As a result of such a distortion and/or deflection, it can be seen that the loading on the bearing and seal 30 has shifted from a uniform radial loading of the bearing and seal 30 to one that is located predominantly radially inwardly and against the sealing surface 36. Because the sealing surface 36, and not the bearing pad 38 is receiving a substantial portion of the loading for which it was not intended, accelerated wear can result.
The present invention is directed to overcoming one or more of the above problems.